Monolithic biocatalytic systems with enhanced stabilities constructed through biomimetic silicification-induced enzyme immobilization on rGO/FeOOH hydrogel

In this study, we present a green and facile method of utilizing biomimetic silicification to trigger enzyme immobilization on the surface of the rGO/FeOOH hydrogel for constructing stable monolithic biocatalytic systems. In brief, the rGO/FeOOH hydrogel is firstly prepared through metal ion-induced reduction/assembly of graphene oxide (GO) nanosheets, which is then utilized to adsorb cationic polyethyleneimine (PEI). This cationic PEI, as the mineralization-inducing agent, catalyzes the condensation of silicate to form silica (biomimetic silicification) on the rGO surface, where enzyme is simultaneously entrapped. The resultant rGO/FeOOH/silica hydrogel shows an extraordinary three-dimensional (3D) porous structure. The silica content on the rGO surface can be facilely tailored through changing the silica precursor concentration. Combined with monolithic macroscale of the rGO/FeOOH/silica hydrogel, the acquired monolithic biocatalytic systems display easy recyclability and elevated pH/thermal/recycling/storage stabilities during the catalytic production of 6-aminopenicillanic acid (6-APA) in comparison to enzyme in free form and enzyme adsorbed on rGO/FeOOH hydrogel. Notably, the activity can be retained up to 93.3% of its initial activity after 11 reaction cycles for our biocatalytic systems.